Rapid mixing granulator or high shear mixing granulator is used in pharmaceutical industries for the mixing and kneading stages of wet granulation. It is a high-speed mixer which ensures uniform mixing of powders and excellent quality of granules are produced in a short period.
It works on the principle of shear.
Parts of Rapid Mixing Granulator
Rapid mixing granulator has the following important parts,
- Mixing Bowl
- Pneumatic Sealing System(Lid)
- Binder Solution Hopper
- Impeller Blades
- Discharging Port
- Wet Mill
Rapid mixing granulator consists of a mixing bowl made of stainless steel grade 316L because it is in direct contact with the product. Mixing Capacity of the bowl varies according to the design and model of rapid mixing granulator.
Pneumatic Sealing System
The mixing bowl is covered by the stainless steel lid. The rotation of the lid is controlled by the air system. The lid is sealed over the mixing bowl by an air sealing system. This air seal tightly closes the lid and there are no chances of product leakage during dry mixing.
Binder Solution Hopper
On the top of the lid, binder or solvent hopper is installed which has a valve or spray system to add binder over powder mix. Binder solution or solvent is added in the hopper and is sprinkled over the powder in a controlled rate.
In conventional rapid mixing granulators, the binder solution is poured over the powder which may result in local over-wetting but in advance mixing granulators a spray system is installed to spray, binder over the powder. The spray rate is controlled by the peristaltic pump.
Impeller blades are usually installed at the bottom of the mixing bowl. Usually, three blades are attached with curved edges. The impeller blades rotate at different speeds by a motor installed at the lower part of the rapid mixing granulator. Speed or rpm of impeller blades vary depending upon design and model of rapid mixing granulator.
Impeller blades ensure uniform mixing of dry powders and spread binder solution or solvent uniformly over the powders and mix the wet mass.
Chopper is installed on the side wall of the mixing bowl. Chopper blades rotate at high speed and act as a cutter. A separate motor is installed in the rapid mixing granulator for the rotation of the chopper. Chopper blades break down the large lumps which are formed during the wetting stage of wet granulation. As the speed of chopper is increased the cutting performance of chopper is also increased.
A discharging port is attached to the side of the mixing bowl of a high shear mixing granulator. It is used to discharge the wet mass and the mass is delivered to the wet mill. The opening and closing of the discharging port are controlled by the air supply system.
Wet mill is attached to the rapid mixing granulator below the discharging port. Wet mass discharged by the discharging port is passed through the wet mill. Stainless steel mesh is attached to the wet mill. Usually, 6 or 8 number mesh is used. The surface area of the wet mass is increased after passing through the wet mill and it facilitates the drying process.
A stainless steel vent filter or breathing filter is attached to the upper side of the lid. It is for releasing the inner pressure built in the mixing bowl during the wet granulation process.
The HMI or human-machine interface is attached to the side of the Rapid mixing granulator. All the parameters like rpm of impeller blades, chopper blades, opening and closing of the lid and wet mill operation are controlled through HMI.
Working Of Rapid Mixing Granulator
The sieved materials to be granulated are added into a rapid mixing granulator for pre-mixing. Sieved materials are added manually by removing the lid or in some advanced type of rapid mixing granulators, dry powers are transferred by a pneumatic system.
For automatically closed transferring, the suction pipes are placed in containers of the product which transfer product from containers to the mixing bowl of the rapid mixing granulator.
After the addition of powders into the mixing bowl, powders are mixed with the help of impeller blades. The speed of impeller blades should be optimum for uniform mixing. Dry Mixing time is usually 10-30 minutes.
After dry mixing, a binder solution or solvent is added into the dry mix through a binder solution hopper. The binder addition rate should be optimized to prevent local overwetting. In advance, rapid mixing granulators solvent hopper is replaced by a spray system which delivers binder solution or solvent at a controlled rate. The solvent or binder solution converts powders into granules and large lumps are formed during the wetting stage. To break down the large lumps chopper is used. Chopper blades break down the large lumps and ensure uniform distribution of binder solvent.
The wet mass formed is passed through the wet mill and the product is ready for drying.
- Stages of Tablet compression.
- Use of starch in wet granulation.
- Methods to determine the endpoint of the wet granulation.
- Lux level in pharmaceutical industries.
- Circulation of purified water in a loop system.